Methods and Apparatus for Manufacturing Micro- and/or Nano-Scale Features

ABSTRACT

The present invention provides devices for generating scalable patterned features on a substrate. In some embodiments, the device includes a means for forming and ejecting a succession of droplets, a charge tunnel, a quadrupole mechanism, a means for reducing the size of one or more of the droplets and one or more stream deflectors.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §120 to, and is adivisional application of, U.S. patent application Ser. No. 12/732,435,filed Mar. 26, 2010, which claims the benefit of priority under 35U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No.61/163,484 filed Mar. 26, 2009, the disclosure of each of which isincorporated by reference herein in its entirety.

GOVERNMENT SUPPORT

Aspects of this research were supported by the NSF-CAREER Award No.0846562. The U.S. Government has certain rights to this invention.

FIELD OF THE INVENTION

The present invention generally relates to the field of micro andnano-scale manufacturing.

BACKGROUND OF THE INVENTION

There exists a need for developing a micro/nano manufacturing processthat has the ability to fabricate selective features at both the microand nano scale. Also, such processes should be able to buildmulti-material features at scalable lengths (nano to micro scale ranges)extemporaneously.

The ability to fabricate structures from the micro to the nano-scalewith varied geometry and high precision in a wide variety of materialsis important in advancing the practical impact of micro andnano-technology.

Manufacturing of micro and nano-sized features has been achieved byusing both contact and non-contact based technologies. However, whencontact based technology is used, there is a possibility ofcontamination of the substrate from the tools. In addition, most knownprocesses involve pre and post processing operations that are timeconsuming and may release hazardous material. Non-contact basedprocesses, such as Pulse Laser Deposition (PLD) and MagnetronSputtering, usually involve masking and may not be able to buildselective features when needed.

SUMMARY OF THE INVENTION

Aspects of the present invention include the application of a controlledheat flux around a microdroplet periphery. A customized direct-writeinkjet system equipped with a resistive heating ring fixture and atemperature proportional integral derivative (PID) controller may beemployed. Additionally, a laser source with variable power modulationcontrol may be employed. Controlled evaporation of mondispersedmicrodroplets to submicron and nanoscale dimensions can be achieved toprovide the basis for generating particulate loaded (i.e., colloids,nanotubes, bio-media and the like) droplets for applications in microand nanomanufacturing in the semiconductor, biotechnological andindustrial sectors.

Thus, according to some embodiments of the present invention, providedherein are methods of generating scalable patterned features on asubstrate. The methods comprise (1) ejecting a succession of droplets;(2) applying a force to the droplets in a manner such that the dropletstravel along a designated path; (3) altering the properties of dropletsin a manner so as to adjust the size of the droplets from micrometer tonanometer; and (4) depositing droplets on the substrate to generatepatterned features on the substrate.

In some embodiments, the patterned features are three-dimensional. Inanother embodiment, the methods described herein further compriserepeating steps (1), (2) and/or (3) at least once. In one embodiment,the ejecting step comprises selectively applying a force to a stream offluid such that the stream breaks into a succession of monodisperseddroplets. In another embodiment, the ejecting step further comprisesvarying the properties of the force to control the characteristics ofthe droplets.

In one embodiment, the ejecting step comprises providing a piezoelectricnozzle, wherein a piezoelectric disk is located in the nozzle.

In one embodiment, the ejecting step provides droplets in the size ofmicrons. In another embodiment, the applying step comprises charging thedroplets. In a different embodiment, the altering step comprisesapplying a heating or laser source to the droplets.

According to another aspect of the present invention, an apparatus forgenerating scalable patterned features on a substrate is provided. Theapparatus comprises (1) a means for droplet forming and ejecting asuccession of droplets; (2) a means for altering the properties ofdroplets in a manner so as to adjust the size of the droplets frommicrometer to nanometer; and (3) one or more stream deflectors tocontrol the direction of the droplets to generate patterned features onthe substrate. Yet, according to some embodiments of the presentinvention, an apparatus comprises (1) the continuous ink jet, (2)quadrupole assembly, and one or more stream deflectors.

Objects of the present invention will be appreciated by those ofordinary skill in the art from a reading of the Figures and the detaileddescription of the embodiments which follow, such description beingmerely illustrative of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. Aspects of the invention may be better understood byreference to one or more of these drawings in combination with thedetailed description of specific embodiments presented herein.

FIG. 1 is a schematic illustration of the apparatus of micro/nanomanufacturing process.

FIG. 2 is a schematic showing of the geometry of a linear quadrupolewith hyperbolic electrodes.

FIGS. 3 a-3 d show results of experiments comparing temperature andvolume reduction for candidate fluids acetone and water.

FIGS. 4 a-4 b shows results of experiments comparing evaporationcharacteristics for candidate fluids acetone and water.

FIG. 5 shows results of experiments comparing evaporationcharacteristics for candidate fluids acetone and water based uponsurface-to-volume ratio of microdroplets.

DETAILED DESCRIPTION

The foregoing and other aspects of the present invention will now bedescribed in more detail with respect to the description andmethodologies provided herein. It should be appreciated that theinvention can be embodied in different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art.

The terminology used in the description of the invention herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of the invention. As used in the description ofthe embodiments of the invention and the appended claims, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. Also, as usedherein, “and/or” refers to and encompasses any and all possiblecombinations of one or more of the associated listed items. Furthermore,the term “about,” as used herein when referring to a measurable valuesuch as an amount of a compound, dose, time, temperature, and the like,is meant to encompass variations of 20%, 10%, 5%, 1%, 0.5%, or even 0.1%of the specified amount. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. Unless otherwise defined,all terms, including technical and scientific terms used in thedescription, have the same meaning as commonly understood by one ofordinary skill in the art to which this invention belongs.

All patents, patent applications and publications referred to herein areincorporated by reference in their entirety. In case of a conflict interminology, the present specification is controlling.

Provided herein, according to some embodiments of the invention, aremethods of generating scalable patterned features on a substrate. Themethods comprise (a) ejecting a succession of droplets; (b) applying aforce to the droplets in a manner such that the droplets travel along adesignated path; (c) altering the properties of droplets in a manner soas to adjust the size of the droplets and (d) depositing droplets on thesubstrate to generate patterned features on the substrate. In someembodiments, during the altering step (c), the size of the droplets isadjusted from micrometer to nanometer.

In some embodiments, the patterned features are three-dimensional. Inanother embodiment, the droplets comprise colloids of one or morematerial. Any applicable material may be used in the present invention.In some embodiments, the material is selected from the group consistingof metal, ceramics, fiber glass, semiconductors, polymers, bio-media(for example, drugs, cell lines, growth factors, and the like), aprecursor solution for sol-gel process and a combination thereof. Insome embodiments, the droplets are deposited via hydrophobic orhydrophilic patterns. In other embodiments, the droplets comprisepolymer fluid.

In another embodiment, the methods further comprise repeating steps (a),(b) and/or (c) at least once. For example, a second or more tiers ofdroplets may be deposited to build multiple layers of nano or microsized features. In some embodiments, the multiple application ofdepositing droplets may provide three-dimensional patterned features.

In one embodiment, the method further comprises the step of curing orgelation of the droplets after steps (a)-(c). In some embodiments, thestep of curing may be carried out by adding chemical additives, exposingto ultraviolet radiation and/or electron beam or heat. In someembodiments, the method further comprises a curing or gelation processfor polymer fluids. For example, an ultra violet curing process and/orgelation may be adopted for polymer fluids.

In some embodiments, the methods of the present invention furthercomprise heating the substrate to remove a solvent. For example, whenthe droplets are deposited via a solution and after the fluid dropletsare deposited, the substrate may be soft-baked in-situ on a hot plate toremove volatile solvents and consolidate the deposited layer.

As used herein, “curing” is a process by which a polymer is toughened orhardened by cross-linking of polymer chains, brought about by chemicaladditives, ultraviolet radiation, electron beam and/or heat.

Stage 1-Ejecting Step (a)

In some embodiments, the ejecting step comprises selectively applying aforce to a stream of fluid such that the stream breaks into a successionof droplets. In one embodiment, the ejecting step further comprisesvarying the properties of the force to control the characteristics ofthe droplets. In another embodiment, the ejecting step comprisesproviding a piezoelectric nozzle, wherein a piezoelectric disk may belocated in the nozzle. Yet, in one embodiment, the force may be appliedto the disk, and the force may be controlled to adjust the size,velocity and/or the ejecting rate of droplets.

In another embodiment, the ejecting step may be performed by a dropletforming mechanism that includes a customized inkjet setup. Thecustomized inkjet set up may further include a continuous inkjet setupas known and described in, for example, U.S. Pat. No. 6,863,385 and U.S.Pat. No. 6,509,917, which are incorporated by reference in theirentireties.

In some embodiments, the droplet forming mechanism may include apiezoelectric nozzle assembly where a stream of fluid is supplied at ahigh pressure (e.g. 5 to 50 psi). A piezoelectric disk may be located inthe piezoelectric nozzle assembly and vibrates at high frequencies (e.g.from 1 KHz to 1 MHz) to generate acoustic waves. In some embodiments,the voltage and frequency of excitation of the piezoelectric disk may bevaried. For example, increasing the voltage applied to the disk mayresult in a higher amplitude of vibration, and the fluid may break intolarger droplet sizes. Another example is when a higher frequency ofpiezoelectric disk excitation is applied, the droplets may have a higherrate, and therefore, the temporal dimension is controlled.

In a different embodiment, the ejecting step further comprisescontrolling the orifice diameter of the nozzle to adjust the dimensionof the droplets. In one embodiment, the ejecting step provides dropletsin the size of microns. In some embodiments, the size of the nozzle maybe varied from 100 microns to a few microns (for example, 1-10) based onthe orifice diameter. In another embodiment, the spatial dimension ofthe droplets may be adjusted by varying the orifice diameter of thenozzle. In other embodiments, droplets may be generated at micrometersizes during the ejecting step and then reduced to nanometer size in thelater stage, for example step (c) the altering step.

In the present invention, the properties that affect droplet formationinclude, but are not limited to, viscosity and surface tension of thestream of fluids provided to the piezoelectric nozzle assembly. Forexample, fluids with higher viscosity may require higher voltages forexciting the piezoelectric disk; fluids with higher surface tensionproperties may require higher excitation of the piezoelectric disk toform consistent monodispersed microdroplets.

Stage 2-Applying (b) and Altering Steps (c):

In some embodiments, the applying step comprises charging the droplets.In another embodiment, the altering step comprises applying a heating orlaser source to the droplets.

In some embodiments, a quadrupole mechanism may be used to guide thedroplets in a straight line path. The exemplary quadrupole mechanism isdescribed in Heston, Stephen F, Linear quadrupole focusing for highresolution Micro-droplet-based fabrication, MS theses, Mechanicalengineering, University of Pittsburgh, 2002. The properties of thedroplets may be altered during their path of flight. Several mechanismsincluding, but not limited to, resistive heating and laser-based curing,may be employed to change the physical, magnetic and electric propertiesof the droplets during path of flight. For example, if a heat source isused, the heat intensity may be controlled to reduce sizes of dropletsfrom micrometer to nanometer by evaporating the solvent. If the heatsource is not applied, the droplet size may remain within the micrometerrange with reduction in size only due to evaporation effect. In otherembodiments, the magnetic and electrical properties of droplets may beadjusted by changing the laser wavelengths, pulse width (i.e., duration)and/or source intensity. Other applicable parameters of dropletsinclude, but are not limited to, fluid properties such as viscosity,density, surface tension, conductivity and/or percent solids (particleconcentration) in solvent base colloids. In some embodiments, the heator laser source may be attenuated or switched off to obtain micrometerto sub-micrometer features.

In some embodiments, a linear quadrupole system may be used to focus thecharged microdroplets and manipulate their fluid properties. Theassociated stability conditions may be predicted from the governingconditions (See Rayleigh, On the Equilibrium of Liquid Conducting MassesCharged with Electricity, Phil. Mag., Vol. 5, 14, 184-186, at 1882.). Alinear quadrupole comprises four electrodes with their axes at thecorners of a square. By connecting the electrodes and applying ACvoltage across adjacent rods, particles of a certain charge to massratio may be focused during their path of flight. The focusingquadrupole will allow an interval in which the properties of the dropletmay be altered for additive fabrication.

For a droplet with radius α₀, surface tension y and charge Q, thespherical shape remains stable as long as the fissility X is less thanone.

$X = {\frac{Q^{2}}{64\pi^{2}ɛ_{0}\gamma \; a_{0}^{3}} < 1}$

-   To prevent the spontaneous disintegration of droplets due to    electrostatic repulsion of the like charges residing on the surface    of the droplet, the AC voltages on the quadrupole electrodes may be    adjusted to stay below the Rayleigh limit. Another method of    controlling the charge on droplets is to vary the charge potential    being impressed by the charge tunnel when the droplets are initially    charged when they exit from the nozzle orifice as described in stage    1.

Stage 3 Depositing Step (d)

In one embodiment, the droplets are charged and the depositing stepcomprises deflecting charged droplets to generate patterned features onthe substrate. In some embodiments, the deflection of the chargeddroplet depends on the strength of the electric field through which ittravels. The equations of motion for a charged droplet traveling throughan electric field of intensity E are given as:

${{m\frac{\upsilon_{x}}{t}} = {{QE} - {D\; \sin \; \theta}}},{{m\; \frac{\upsilon_{z}}{t}} = {{m\; g} - {D\; \cos \; \theta}}},$

If the undeflected droplet stream is aligned with the z coordinate whichis parallel to the gravity vector, and the magnitude of the deflectionis measured in the perpendicular x coordinate. Here vx and vz are thecomponents of velocity in the x and z coordinates. In the above, g isthe gravitational acceleration, and D is the aerodynamic drag force.

Fillmore [1977] predicted the deflection distance as:

${x_{d} = {\frac{QE}{m\; \upsilon_{0}^{2}}{l_{dp}( {z_{p} - \frac{l_{dp}}{2}} )}}},$

Where Q is charge, m is mass, v_(o) is initial stream speed, x_(d) isthe deflection of a droplet, z_(p) is the distance from the deflectionplate entry to the substrate, and l_(dp) is the length of the deflectionplates. The prediction neglects the effects of gravity, drag, and/ormutual electrostatic interactions.

In other embodiments, the placement of droplets may be controlled by thepositioning of the substrate. The crystal growth, material compositionand morphology of the droplets may be controlled by the temperaturegradients around the droplets and may be adjusted by the heating-coolingcycles.

According to some aspects of the present invention, the methodsdescribed herein may be used to selectively manufacture heterogeneousstructures both in terms of geometry and material composition. In someembodiments, the methods described herein may further comprise substratetreatments. For example, sintering, curing, or other functionalizing,may be performed on the features.

As one of ordinary skill in the art may appreciate, the parametersdescribed herein may vary greatly depending on the material/droplets.Such modifications are known to those skilled in the art.

Apparatus

Another aspect of the present invention provides an apparatus forgenerating scalable patterned features on a substrate. The apparatuscomprises (1) a means for droplet forming and ejecting a succession ofdroplets; (2) a means for altering the properties of droplets in amanner so as to adjust the size of the droplets from micrometer tonanometer; and (3) one or more stream deflectors to control thedirection of the droplets to generate patterned features on thesubstrate.

In one embodiment, the means for droplet forming may be selected from acontinuous ink jet (CIJ), drop-on-demand (DOD) or thermal inkjet (TIJ)method. In another embodiment, the continuous ink jet comprisespiezoelectric nozzle assembly. Yet, in a different embodiment, thepiezoelectric nozzle assembly comprises a piezoelectric disk. In oneembodiment, the means for altering the properties of droplets comprisesa charge tunnel and a quadrupole assembly. In another embodiment, themeans for altering the properties of droplets further comprise aheating, laser source, or a combination thereof.

The present invention will now be described in more detail withreference to the following examples. However, these examples are givenfor the purpose of illustration and are not to be construed as limitingthe scope of the invention.

EXAMPLES Example 1 Stage 1—Customized Continuous Inkjet-BasedMicrodroplet Generation

As shown in FIG. 1, a customized continuous inkjet (CIJ) setup may beutilized to generate microdroplets. Fluid is supplied at a high pressure(5 to 50 psi) to a piezoelectric (PZT) nozzle assembly to generate afluid jet. A piezoelectric disk located within the PZT nozzle assemblyvibrates at high frequencies (variable from 1 kHz to 1 MHz) generatingacoustic waves. A combination of Rayleigh instabilities and forcedacoustic waves create standing nodes on the surface of the ejected jet,causing it to break up into fine droplets. (See Rayleigh, On theInstability of Jets, Proceedings of the London Mathematical Society, 10(4), 4-13 (1878), Depending on the fluid properties, piezoelectric diskexcitation parameters and nozzle geometry, droplet diameters can varyfrom 1 to 2.5 times the nozzle orifice diameter. The inkjet processdescribed above involves a complex interaction of three domains:electrostatic, structural, and fluid. More importantly, the dropgeneration mechanism occurs at particular spatial and temporaldimensions. For example, at 1 MHz frequency each drop is formed ataround 1 microsecond and can have dimensions to the order of 1-5 μm.Further, each droplet is charged before break-off from the jet in acharge tunnel. These charged droplets are fed to a quadrupole mechanism.

Stage 2—Quadrupole Mechanism

As shown in FIG. 1, the quadrupole mechanism acts as a guide way toconstrain the path of the droplet motion. It consists of four electrodesarranged with their axes at right angles to each other. By connectingthe electrodes, as shown in FIG. 2 and applying an AC voltage acrossadjacent electrodes, charged fluid microdroplets of a certaincharge-to-mass ratio are focused as they travel through the electrodelength. The constrained motion of the microdroplets allows for asufficient time interval in which the properties of the droplets can bealtered during their path of flight. The droplet may be adjusted from amicrodroplet (1 to 5 μm) to a nanodroplet (80 to 200 nm).

Stage 3—Deflector Plate Mechanism

As shown in FIG. 1, on exit from the quadrupole mechanism the droplet isdeflected onto the substrate using a deflector plate mechanism. Thismechanism consists of two high voltage plates which deflect the dropletbased on the potential equilibrium. These deflector plates can becharged at variable voltages depending on the droplet pattern to begenerated on the substrates. The principle of electric field baseddeflection of charged particles is described in U.S. Pat. No. 6,509,917,which is incorporated by reference in its entirety.

Example 2 Comparison of Different Fluid Types

Nanopure distilled water and 99.998% filtered acetone were the twofluids used as candidate fluids with specific heats of 75.33 and 126.66(J/mol·K) respectively. This comparison enabled the assessment of thesignificance of specific heat of fluids (e.g., low vs. high) on dropletevaporation. The other factor investigated was the impact of nozzlediameter (50 μm vs. 30 μm), which can determine the effect of surface tovolume ratio on droplet evaporation. Both fluids were jetted using acustomized direct-writing inkjet system (MicroFab Technologies Inc.,Plano, Tex.). The system included a JetDrive III waveform generator andamplifier, a pneumatics console, optics system and a MJ-AT-01-30piezoelectric (PZT) microvalve with an interchangeable orifice (i.e.,nozzle) diameter of 30 and 50 μm, Monodispersed microdroplets weregenerated and subjected to convective heat flux using a resistiveheating ring fixture (Mid Atlantic Heater and Control Inc., S.C.)equipped with a controller.

The experimental conditions included jetting both fluids (water andacetone) from two different nozzle diameters (30 μm and 50 μm). Thetemperature of the resistive heating ring fixture was adjusted toevaporate the droplets from each experimental condition as shown inTable 1 below. The initial droplet condition (i.e., without the heatingring) for each experiment was recorded at room temperature (25° C.). Thereductions in droplet for temperatures from 200° C. to 400° C. inincrements of 50° C. were recorded.

TABLE 1 Experimental Conditions Condition Nozzle Ring temperature No.Diameter Fluid type range (° C.) 1 50 microns Acetone 200-400 2 30microns Acetone 200-400 3 50 microns Distilled water 200-400 4 30microns Distilled water 200-400

A charge coupled device (CCD) camera with a microscopic zoom lens wasemployed to capture microdroplet formation and their trajectories duringtheir path of flight as they were jetted from the nozzle orifice. Alight emitting diode (LED) source was synchronized with thepiezoelectric actuator to provide illumination for observing thedroplets. Once a stable monodispersed droplet condition was achieved,the heating ring fixture was positioned to envelope the droplets forevaporation. Image acquisition software (ImageJ) from the NationalInstitute of Health (NIH) was used to analyze the droplet evaporation. Acopper wire with predefined dimension was introduced in the frame duringimage capture to calibrate the microdroplet dimensions. Droplet surfacearea and volume were calculated for each experimental condition toobserve reduction in its size with variations in the temperature.

Percentage Reduction in Droplet Volume

For each of the four experimental conditions, a proportionalrelationship between percentage volume reduction and incrementaltemperature (shown in FIG. 3) was observed.

A 50 μm nozzle size yielded higher percentage reductions in volume overthe 30 μm nozzle size for both the fluid types.

Effect of Fluid Type

Based on the fluid type, acetone was observed to evaporate at a higherrate with an increase in the temperature as shown in FIG. 4.

Effect of Surface Area to Volume Ratio

The effect of surface to volume ratio on droplet evaporation wasobserved as shown in FIG. 5. Fluids when jetted through smaller nozzlessize resulted in higher surface to volume ratio and vice versa. However,as the temperature increased, a 50 μm acetone droplet evaporated at muchfaster rates than the 30 μm size droplets resulting in highersurface-to-volume ratio at higher temperatures.

In conclusion, the droplet evaporation characteristics for water andacetone were studied to understand the microdroplet size reductionphenomenon. A proportional reduction in the volume of the microdropletsof water and acetone was observed with an increase in heat flux. Acetonemicrodroplets exhibited more percentage volume reduction compared tothat of water under the same conditions. Also for both fluids, dropletsjetted with the 50 μm diameter nozzle were observed to have higherpercentage volume reductions than those jetted with the 30 micronnozzle. Droplets with higher surface area to volume ratio evaporated ata faster rate.

REFERENCES

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9. Taflin et al., Electrified Droplet Fission and the Rayleigh Limit,LANGMUIR, 5:376384 (1989).

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11. Gomez and Tang, Charge and Fission of Droplets in ElectrostaticSprays, PHYS. FLUIDS 6:404414 (1994).

12. Choi and Kim, Experimental evaluation of electrodynamically focusednanoparticle behavior in the quadrupole electric field, AnnualConference of the American Association for Aerosol Research (2007),

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14. Schneider et al., Stability of an electrified liquid jet, J. APPL.PHYS. 38(6):2599 (1967).

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The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. Although a few exemplary embodiments ofthis invention have been described, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe claims. The invention is defined by the following claims, withequivalents of the claims to be included therein.

1. An apparatus comprising: (1) a means for forming and ejecting asuccession of droplets; (2) a charge tunnel; (3) a quadrupole mechanism;(4) a means for reducing the size of one or more of the droplets; and(5) one or more stream deflectors.
 2. The apparatus of claim 1, whereinthe means for forming and ejecting a succession of droplets isconfigured to selectively adjust the size, velocity and/or ejection rateof the droplets.
 3. The apparatus of claim 1, wherein the means forforming and ejecting a succession of droplets comprises a continuous inkjet apparatus, a drop-on-demand inkjet apparatus or a thermal inkjetapparatus.
 4. The apparatus of claim 1, wherein the means of dropletforming and ejecting a succession of droplets comprises a piezoelectricnozzle.
 5. The apparatus of claim 4, wherein the piezoelectric nozzlecomprises a piezoelectric disk.
 6. The apparatus of claim 5, wherein themeans for forming and ejecting a succession of droplets is configured toselectively vary a voltage of excitation of the piezoelectric disk. 7.The apparatus of claim 5, wherein the means for forming and ejecting asuccession of droplets is configured to selectively vary a frequency ofexcitation of the piezoelectric disk.
 8. The apparatus of claim 5,wherein the means for forming and ejecting a succession of droplets isconfigured to selectively vary an orifice diameter of the piezoelectricdisk.
 9. The apparatus of claim 1, wherein the charge tunnel isconfigured to apply a variable charge potential to the droplets.
 10. Theapparatus of claim 1, wherein the quadrupole mechanism is configured toguide the droplets in a straight line path.
 11. The apparatus of claim1, wherein the quadrupole assembly comprises four electrodes wherein theelectrodes are arranged with their axes at right angles to each other.12. The apparatus of claim 1, wherein the means for reducing the size ofone or more of the droplets is configured to reduce the size of one ormore of the droplets by at least about 20%.
 13. The apparatus of claim1, wherein the means for reducing the size of one or more of thedroplets is configured to reduce the size of one or more of the dropletsfrom 1 to 5 μm to 80 to 200 nm.
 14. The apparatus of claim 1, whereinthe means for reducing the size of one or more of the droplets comprisesa heat source.
 15. The apparatus of claim 1, wherein the means forreducing the size of one or more of the droplets comprises a lasersource.
 16. The apparatus of claim 1, wherein the one or more streamdeflectors comprise two plates, each of which is charged.
 17. Anapparatus, comprising: (1) a means for forming and ejecting a successionof droplets, comprising a piezoelectric nozzle; (2) a charge tunnel; (3)a quadrupole mechanism; (4) a means for reducing the size of one or moreof the droplets, comprising a heat source, a laser source or acombination thereof; and (5) two or more charged deflector plates. 18.The apparatus of claim 17, wherein the piezoelectric nozzle comprises apiezoelectric disk.
 19. The apparatus of claim 17, wherein the means forforming and ejecting a succession of droplets is configured toselectively vary: (a) a voltage of excitation of the piezoelectric disk;(b) a frequency of excitation of the piezoelectric disk; and/or (c) anorifice diameter of the piezoelectric disk.
 20. The apparatus of claim19, wherein the means for reducing the size of one or more of thedroplets is configured to reduce the size of one or more of the dropletsby at least about 20%.